1. Field of the Invention
This invention is in the field of chemical syntheses and relates in particular to the synthesis of anthrapyridones.
2. The Prior Art
4-Aminoanthrapyridones were first reported as a red chromophore class in 1932 SANDOZ U.S. Pat. No. 1,891,317. These dyes were prepared by an acylationaldol condensation (cyclization) sequence between a 1-amino-4-haloanthraquinone and an acylating agent possessing at least two reactive .alpha.-hydrogens (e.g., esters of acetoacetic or malonic acid, or acetic anhydride), followed by displacement of the relatively reactive halogen in Ullmann fashion with an appropriate amine. The harsh reaction conditions (time, temperature, pH) generally employed for the acylation and ring-closure steps of anthrapyridone preparation have resulted in yields that vary dramatically from chromophore to chromophore depending on the nature and sensitivity of the functionality involved.
Other representative older references to anthrapyridones and their syntheses which demonstrate the harsh reaction conditions heretofore employed include: (a) "British Intelligence Objectives Subcommittee Report 1484", Publication Board No. 86139, Library of Congress, Washington, D.C., 1947, p. 46; (b) C. F. H. Allen, J. V. Crawford, R. H. Sprague, E. R. Webster, and C. V. Wilson, J. Am. Chem. Soc., 72, 585 (1950); (c) Brevet D' Invention 827,961 (I.C.I., 1938); (d) British Pat. No. 964,602 (I.C.I., 1964); and (e) German Patentschrift No. 658,114 of I. G. Farben.
More recently, anthrapyridones took on a new interest to us when it was discovered that such groups were especially advantageous as polymeric dye chromophores [See D. J. Dawson, K. M. Otteson, P. C. Wang, and R. E. Wingard, Jr., Macromolecules, 11,320 (1978)].
Commonly assigned U.S. Pat. No. 4,182,885 issued on Jan. 8, 1980 to Bunes disclosed a family of red polymeric aminoanthrapyridone dyes having a chromophore of the formula ##STR1## =polymer backbone
These dyes can be prepared by the Ullmann condensation of 3'-phenyl-2-methyl-4-bromoanthrapyridone (6, Br-PAP) or a 3'-phenyl substituted Br-PAP with an amine containing polymer.
Br-PAP can be prepared from 1-amino-2-methyl-4-bromoanthraquinone (4, AMBAX), an intermediate available commercially (SANDOZ), or made from 2-methylanthraquinone (1, 2-MAX), an intermediate also available commercially (BASF). Reaction Scheme I details this possibility. ##STR2##
In early studies, AMBAX, was acylated with penylacetyl chloride (PhCH.sub.2 COCl) in toluene or diglyme at reflux to give compound 5 (PAMBAX), which was then with or without isolation cyclized to Br-PAP with refluxing aqueous base. This process had a number of drawbacks. The most important of these were: (a) serious agitation problems were encountered during the cyclization because of reaction heterogeneity; (b) the yield, because of unavoidable side-reactions during the acylation, was apparently limited to about 70%; and (c) plant-scale production runs contained varying amounts of 3'-phenyl-2-methyl-4-chloroanthrapyridone as a contaminant (produced by a proton-catalyzed chloride for bromide exchange during the acylation).
The next phase of Br-PAP work resulted in the discovery that AMBAX and 1.25 equivalents of phenylacetic acid (PhCH.sub.2 CO.sub.2 H) could be combined in pyridine (65.degree. C./2 hours) under the aegis of TiCl.sub.4 to directly produce Br-PAP in yields of approximately 80%. Although this process was clearly superior to the earlier processes at the bench and, in addition, it substituted the less expensive, less toxic, more stable, and more readily available PhCH.sub.2 CO.sub.2 H for PhCH.sub.2 COCl, it failed for several economic and safety reasons to qualify as an industrially feasible process. It is the subject of U.S. Pat. No. 4,309,543 issued Jan. 5, 1982.
It is therefore an object of this invention to provide an improved chemical process for the manufacture of anthrapyridone materials such as Br-PAP which avoids the harsh reaction conditions and low isolated yields of the prior art processes.